Production of acrylonitrile polymer fibers



United States Patent 3,399,260 PRODUCTION OF ACRYLONITRILE POLYMERFIBERS Kazumi Nakagawa, Saidaiii, Nobuhiro Tsutsui, Okayama, and .lunjiTsuge, Saidaiji, Japan, assignors to Japan Exlan Company Limited, Osaka,Japan No Drawing. Filed May 27, 1964, Ser. No. 370,722 Claims priority,application Japan, June 5, 1963, 38/29, 445 3 Claims. (Cl. 264182)ABSTRACT OF THE DISCLOSURE A method of producing acrylonitrilic polymerfibers is provided, which comprises coagulating a spinning solution soas to form coagulated gel fibers, treating such fibers in a hot medium,stretching the fibers, and water-washing and drying them.

The present invention relates to a method of producingpolyacrylonitrile-ty-pe fibers and particularly to a Wetspinning methodof producing dense polyacrylonitrile-type fibers having smooth surfaces,circular cross-sections and a silk-like touch and luster.

The method of the invention, though applicable to the production ofstaple fibers and filaments (long fibers) of acrylonitrile polymers orshaped articles such as films and thin diaphragms thereof, will hereinbe described particularly with reference to the production of fibers.

Fibers composed of acrylonitrile polymers are normally produced byeither a dry-spinning or a wet-spinning method using an appropriatespinning solution which comprises the acrylonitrile-type polymerdissolved in either an organic solvent or a concentrated aqueoussolution of inorganic salt. In wet-spinning, particularly when anaqueous coagulation bath is used, the solvent is diffused outwardly fromthe fibers being coagulated and at the same time the water in thecoagulation bath penetrates into the fibers. This results in such fibershaving spongelike porous structures. In some cases opaque gel fibers areobtained through devitrification. Such porous structures cannot beentirely collapsed in the subsequent processing and are carried throughinto the final fibers thereby adversely affecting the strength,wear-resistant properties and luster of the fibers.

In the ordinary Wet-spinning process, a method is -followed whereinthermal stretching is operated after the removal of the solvent in orderto elfect the collapsing of the voids produced in the fibers duringcoagulation, whereupon the fibers are dried at high temperatures. Eventhis method, however, cannot effect the perfect collapsing of the voidsin some cases (for example, in case of filaments of more than 50deniers). Furthermore, when such a method is used, greater-than-normalstretching is necessary in order to obtain suitable fiber density, withthe result that the fibers after undergoing the usual subsequent hightemperature drying process, become both brittle and poor inwear-resistant properties. For the purpose of improving this undesirablesituation, a slackening treatment usually operated by using heat orsteam is added as an additional process step. Slackening treatment usingsteam is operated under high temperature and pressure, so that aparticular pressure apparatus is required.

An object of the present invention is to provide a method of producingfibers having properties adapted to various fiber applications by makingdense the porous structures inherent as above-stated to the wet-spinningof acrylonitrile polymers, without the necessity of subsequentslackening treatment. Another object of the present invention is toprovide a method of producing acrylonitrile polymer fibers having smoothsurfaces, circular cross-sections and a silk like touch and luster.Other objects and advantages will become clear from the descriptionhereinafter.

The above-stated objects may be achieved by a process comprising thesteps of (1) extruding a spinning solution containing (a) acrylonitrilepolymer and (b) organic solvent or concentrated aqueous solution ofinorganic salt, into an aqueous coagulation bath so as to coagulate itin the form of swelling gel fibers containing water and a small amountof solvent (the above-stated organic solvent or inorganic salt), (2)drying the resultant fibers thereby evaporating the water in the gelfibers, (3) subjecting the same to stretching in a hot medium, (4)washing in water to extract the solvent, and (5) final drying.

The fibers thus obtained are excellent in strength and wear-resistantproperties and have smooth surfaces without any perceptible surfaceirregularity of grooves extending axially of the fibers as would be seenin the conventional wet-spun fibers. Further, the cross-sections of thenovel fibers are of substantially perfect circle, and suchconfigurational features are substantially maintained even in case offibers of 50 to deniers or more. It is impossible not only for theconventional wet-spinning process but also for the conventionaldry-spining process to obtain such desirable results.

Further, a microscopic examination has proved that the fibers madeaccording to the present invention are desirably dense and compact.Generally, when fibers are microscopically viewed under dark field,their minute voids (larger than 0.1 in magnitude) will be observed asbeing small shining spots because they reflect the light, while theother portions of the fibers will look black. When conventional fibersare viewed under dark field, many shining spots, i.e., voids, may beseen but the fibers made according to the present invention have veryfew voids, which fact is evidence that these fibers have practicallyperfectly uniform structures.

To explain the invention more particularly, the acrylonitrile polymersemployed in the invention include polyacrylonitrile (homopolymer), acopolymer, a copolymer of acrylonitrile and at least one kind of othermonoolefin monomer, block polymers, graft polymers and mixtures of saidpolymers. However, it is preferable that the polymers used in theinvention contain at least 40% of acrylonitrile. As monomers other thanacrylonitrile, may be used vinyl acetate, vinyl esters of othermonocarboxylic acids, acrylic acid, acrylic esters such as methylacrylate and ethyl acrylate, methacrylic acid, methacrylic esters suchas methyl rnetharylate, vinyl chloride, vinylidene chloride, styrene,methacrylonitrile, vinylidene cyanide, vinyl pyridine and itssubstituted derivatives, other vinyl substituted nitrogen-containingheterocyclic compounds such as vinyl imidazole, aliphatic and \acromaticsulfonic acids having unsaturated bond such as styrene sulfonic acid,allyl sulfonic acid and methallyl sulfonic acid, and fonoolefin monomerscapable f0 copolymerizing with acrylonitrile.

Solvents used in the present invention would include organic solventshaving higher boiling point than water as N,N dimethyl formamide, N,Ndimethylacetamide, ethylene carbonate and dimethyl sulfoxide, andconcentrated aqueous solutions of such inorganic salts as thiocyanates,e.g., sodium thiocyanate and calcium thiocyanate, perchlorates, e g.,sodium perchlorate and calcium perchlorate, zinc chloride and lithiumchloride.

The spinning solutions obtained by dissolving the abovementionedacrylonitrile polymers in these solvents are transparent, viscoussolutions, and the suitable concentration of polymer varies according tothe kinds of solvents and the molecular weight of polymers, butpreferably is generally more than 7%.

These spinning solutions, after being deaerated and filtered, areextruded through minute holes into the dilute aqueous solution of thesolvent used in dissolving the polymers or into the non-solvent of saidpolymers, thereby permitting the same to coagulate therein. In thisinstance, it is not always necessary for the coagulated gel fibers tohave transparent uniform structures as in case of the usual wet-spinningprocess, because the gel fibers, no matter whether or not they betransparent, will have uniform transparent structures after they havebeen subjected to the subsequent drying process. It is, therefore, notnecessary to pay much attention to the conditions of coagulation and itsis possible to carry out coagulation at room temperature. This is one ofthe outstanding advantages of the present invention.

The gel fibers after coagulation is complete are trans ferred to adrying process while they still contain a fixed amount :of solvent(e.g., the aforementioned organic solvent or inorganic salt) in anamount by weight not exceeding 1.5 times the dry weight of the polymer.The purpose of this drying process is to evaporate the water containedin the gel fibers and thereby correct the gel from a porous structuretype form into a transparent and compact form. It is important that sucha fixed amount of solvent should be contained in the gel fibers at theoutset of this drying step. This permits the gel fibers to be againdissolved and to be converted into a transparent and uniform gel andfinally results in the subsequent stretching process becoming easier tomanage. Generally, it is preferable that the polymer content in thedried gel fibers be more than 30% but if it becomes higher than about90% the stretching step is rendered difiicult.

The amount of solvent to be contained in the dried gel fibers variesaccording to the kinds of solvents and the conditions of stretching. Forexample, where an inorganic salt such as a thiocyanate is used as thesolvent, it is desirable that the ratio ofthe weight of solventcontained in the dried gel fibers to the weight of polymer is less than1.521 and that the ratio of the weight of water to the weight of solventis less than 1.5 :1. Also, where an organic solvent is used, it isnecessary to dry the gel fibers until a condition is attained whereinsolvent alone remains in the gel fibers with no substantial watercontained therein. If the drying temperature is higher a shorter dryingtime is required, but if the temperature is too much higher, uniformdrying is hard to effect. A temperature range of about 40-80 C. issuitable.

The gel fibers made dense by the aforesaid drying step are now stretchedin a medium that will not extract the solvent. Suitable stretchingconditions vary according to the compositions of gel fibers, the kindsof solvents and the physical properties of the intended final fibers.Generally, with higher polymer content in the dried gel fibers,stretching becomes more difficult with the result that high stretchingtemperatures are necessary, and if it is desired to have a higher ratioof stretching, then higher stretching temperatures are required. If thestretching temperatures are very low, the stretched fibers willconsiderably be devitrified and if the stretching temperatures are stilllower, the fibers will be broken, whereupon it is impossible to continuethe stretching operation. Therefore, when certain compositions andstretching ratio are given, there will exist the lowest temperature atwhich the stretching may be successfully carried out. This temperaturemay vary from room temperature up to about 100 C. depending upon the gelcompositions and the stretching ratio. There is a close relationshipbetween the stretching conditions and the final fibers, i.e., generally,the higher the stretching ratio, the higher the strength and the lowerthe elongation. Also, the higher the stretching temperaures the lowerthe strength, the higher the elongation and the more the tenacity isincreased. Therefore, it is necessary to select suitable conditionsaccording to the intended properties.

Any stretching medium may be employed so far as it is inactive withrespect to the dried gel fibers, but such a medium as will extract thesolvent is not preferable. The most generally used medium is air.

In this case, the heat source may be air itself (i.e., heated air).Sources such as heating by the radiant heat such as from an infraredlamp or a heated plate, heating by high frequency or heating by manyother known methods, may also be utilized. Liquid mediums such as willnot extract the solvent may be used. Heating by hot water or water vaporis not suitable. In practice, it is convenient to operate the stretchingsuccessively at the end of the preceding drying process.

The stretched gel fibers are immediately washed in a water bath toextract the solvent is contained in the fibers. The washing temperatureused may be room temperature, but in some cases Washing at hightemperature is operated.

The washed fibers are then, if necessary, passed through such subsequentprocesses as crimping process, finishing agent-applying process, cuttingprocess, etc. and thereafter are dried to produce the final fibers. Thefibers after washing are still of suitable density and their watercontent is remarkably low. Consequently they can be dried at a higherspeed and lower temperature than the ordinary wet-spun fibers.

According to the method of the invention, it is also possible to produceconsiderably heavy denier fibers of more than 50 deniers. When heavydenier fibers are to be spun by the ordinary wet-spinning process, it isvery hard to effect the collapsing of the swelling porous structure formaking the fibers dense or compact. Even if it is effected, there wouldresult grooves and irregularity on the surfaces thereby providingirregular cross-sections. On the other hand, when heavy denier fibersare to be produced by the dry-spinning process, the rate of evaporationwould be low due to the fibers being thick, thus causing difiiculties.Since according to the present invention compacting is easily effectedbefore stretching, the drawbacks in the conventional wet-spinningprocess are eliminated. Also, since a substantial amount of solvent isremoved before compacting is etfected, the removal of solvent which is aproblem with which the conventional dryspinning is confronted, it notnow so critical. Thus the method of the present invention is suitablealso for the production of thick fibers.

If necessary, it is also possible to add to the polymers customaryadditives such as coloring pigments, anti-coloring agents, stabilizer,plasticizers and the like.

The invention will now be described with reference to the examplesthereof, it being understood that the invention is by no means limitedto them.

All the percentage used in the following examples are by weight.

acryl sulfonic acid 10/ 0.75 is dissolved in a 46% aqueous solution ofsodium thiocyanate to prepare a spinning solution having a polymerconcentration of 9%.

This spinning solution is extruded through a spinnerette provided with50 fine holes each having a diameter of 0.065 mm. into a 12% aqueoussolution of sodium thiocyanate kept at 20 C. and is permitted tocoagulate therein. The coagulated gel fibers are then immersed in a bathcontaining a 4% aqueous solution of sodium thiocyanate to permit thesodium thiocyanate concentration of the gel fibers to establish itsequilibrium and thereafter are taken out from said bath. After theremoval of excessive solution from the thus-treated gel fibers, thesefibers are dried in the air at 50 C. for 6 minutes. The gel fibersobtained by said drying step have a composition consisting of about 70%of polymer, 15% of sodium thiocyanate and 15% of water. The dried gelfibers are stretched in heated air at various stretching ratios andstretching temperatures and immediately thereafter are washed undertension in water at room temperature to remove the sodium thiocyanatetherefrom and finally are dried at C. The yarn properties of the fibersthus obtained are shown in Table 1.

TABLE 1 Stretching Stretching Dry Strength Dry elongation Knot strengthKnot elongation No. Ratio tem(pe5a)ture Fineness (d.) (g./d.) (1%)(g./d.) (1%) Appearance 60, 7. 6 2. 46 40. 1. 96 29. 2 Devitrification.80 6. 8 2. 44 47. 1 2. 01 29. 8 Transparent. 100 6. 6 2. 42 47. 8 2. O334. 9 D0. 120 5. 3 2. 51 48. O 2. 23 44.0 Do.

60 9. 4 2. 09 41. 5 1. 61 25. 9 Devitrification. 80 6. 5 2. 95 43. 7 1.94 26. 2 Transparent. 100 5. 8 2. 76 40. 9 1. 97 23. 8 Do. 120 5. 6 2.27 46. 2 2. 00 39. 2 Do.

80 5. 0 3. 32 33. 3 0. 58 5. 9 Devitrafication. 100 4. 1 3. 98 35. 5 1.27 8. 6 Transparent. 120 4. 3 3. 35. 3 2. 68 28. 5 Do.

80 4. 7 2. 98 26. 4 0. 43 5. 7 Divitrification. 100 3. 7 3. 92 29. 9 1.84 15. 5 Transparent. 120 3. 7 3. 57 29. 6 1. 46 14. 1 Do.

As shown m Table 1, the properties of the fibers re- EXAMPLE 3 markablyvary according to the stretching conditions. Generally, the higher thestretching ratio, the higher the dry strength and the lower the dryelongation, the knot strength and the knot elongation. When thestretching temperature becomes higher, the dry strength graduallydiminishes through its maximum value, the dry elongation increases tosome degree and the knot strength and elongation considerably increase.It is, therefore, possible to obtain any desired set of fiber propertiesby suitably selecting the stretching ratio and stretching temperature.The microscopic observation of these samples under dark field will provethat they are very uniform in structure, with very few voids found inthe fibers. In Table 1, the samples of Nos. 1, 5, 9 and 12 aredevitrified since local fracture takes place in the fibers due to theirlower stretching temperatures. At temperatures still lower than these,it would be impossible to stretch the fibers because of their breakage.

EXAMPLE 2 The coagulated gel fibers obtained by the same operation as inExample 1 are immersed in a 5% aqueous solution of sodium thiocyanateand thereafter are dried overnight to obtain gel fibers having acomposition consisting of about 65% of polymer, 18% of sodiumthiocyanate and 17% of water. The gel fibers thus obtained are stretchedin heated air, are Washed in hot water and are A copolymer ofacrylonitrile/methyl acrylate (/10) is dissolved in a 50% aqueoussolution of sodium thiocyanate to prepare a spinning solution havingpolymer concentration of 12%. This spinning solution is extruded througha spinnerette provided with a hole having a diameter of 0.5 mm. into a7.5% aqueous solution of sodium thiocyanate at 15 C. and is permitted tocoagulate therein. The thickness of the resulting gel fibers is about530 deniers. Because the coagulating temperature is not low, the gelfibers are considerably devitrified, but such devitrification does notmatter. Then, the coagulated gel fibers are taken out from the bath.After the removal of the excessive coagulated solution from the gelfibers, these fibers are dried at 50 C. under non-tension and therebyconverted into transparent gels, the composition of which consists of67% of polymer, 20% of sodium thiocyanate and 13% of water. Then, thegels are stretched by 7.1 times in heated air at 105 C., immediatelythereafter are washed in water at room temperature to remove the solventtherefrom and are dried at 105 C. to provide fibers of 98 deniers. It isastonishing that in spite of being as thick as 100 deniers, these fibershave no such irregularity on the fiber surfaces as is seen in the usualconventionally wet-spun fibers and are very smooth with theircross-sections almost perfect circles.

The dry strength of these fibers is 2.18 g./d., their dry finally driedat C. The fiber properties of the result- 4 elongation is 39.5%, theirknot strength is 1.99, and their ing samples are shown in Table 2. knotelongation is 19.5%

TABLE 2 Stretching Stretching Fineness Dry strength Dry Knot Knot ratiotemperature (d.) (g./d.) elongation strength elongation 0.) (percent)(g./d.) (percent) 6.9 100 3. 4 3. 18 38. 5 2. 50 28. 5 3. 3 2. 54 41. 92. 39 40. 2 7.6 100 3. 3 3.18 33. 6 2.64 so. 5 120 3.0 2. 43 36. 4 2. 2030. 9 100 2.8 3. 46 34. 9 2. 43 21.3 120 2. 6 3. 00 4o. 3 2. 34 23. 1

60 EXAMPLE 4 In these samples, the gel fibers when being stretchedcontain a slightly more amount of solvent than in Example 1, so that thestretching is easily operated. Though the fibers were subjected to thesame stretching conditions, the dry strength is somewhat lower but theknot strength is higher.

TABLE 3 Stretching Stretching Fineness Dry strength Dry Knot Knot ratiotemperature (g./d.) elongation strength elongation 0.) (percent) (g./d.)(percent) What we claim is: A v

1. In a method of producing acrylonitrilic polymer fibers byWet-spinning a spinning solution containing an acrylonitrilic polymerdissolved in a concentrated aqueous solution of a thiocyanate assolvent, the improvement comprising coagulatin said spinning solution inan aqueous coagulating bath so as to form coagulated gel fiberscontaining the thiocyanate in an amount of not more than 1.5 times thedry weight of the polymer, treating such coagulated fibers in hot air ata temperature of 40 to 80 C. in order to reduce the water content insaid fibers to not more than 1.5 times the amount of thiocyanatecontained in said fibers, stretching the fibers at a temperature ofabove 40 C. in a medium which will not extract said thiocyanate from thefibers, and subsequently Water-wash- ]5 ing and drying the fibers.

2. The method according to claim 1 wherein said thiocyanate is sodiumthiocyanate.

8 3. Themethodaccording t0 q lw l q fiil l fiq unstretched fiberscontain equal parts of water and sodium thiocyanate and at least 30% byweight of the polymer.

References Cited UNITED STATES PATENTS 3,037,240 6/1962 Stoy 2641823,101,245 8/1963 Fujita et al. 264183 3,180,913 4/1965 Veitch et al.264-182 2,697,023 12/1954 Martin 264--182 2,948,581 8/1960 Cummings264-182 2,984,912 5/1961 Robertson et al. 3,052,512 9/1962 Kocay et al.264-182 FOREIGN PATENTS 38,225 1/1963 Japan.

JAMES A. SEIDLECK, Primary Examiner. J. H. WOO, Assistant Examiner.

